A typical wireless packet includes a synchronization preamble (SHR) portion, a physical header (PHR) portion and a data portion (also called the ‘payload’) transmitted in that order, as illustrated in FIG. 1. The SHR preamble contains a synchronisation field and a start of frame delimiter (SFD). The SHR preamble is used to achieve signal acquisition, signal synchronization and ranging. The SFD is used to detect the end of the synchronisation field, the end of the synchronisation preamble as a whole and the start of the physical header. Hence, the SFD serves as a delimiter between the SHR and the PHR. The PHR is used to provide the receiving system with information concerning the data that will follow, such as an indication of how much data is being sent in the packet and what signalling or protocol is being used to transmit the data or payload.
In general, the more received bits the receiver has available for synchronization, the better, resulting in the data packet being received and interpreted more reliably.
In certain implementations, like in preamble based ultra low power wireless communications, the length of the SFD is normally short to minimize the energy wasted for non-data communication. However, this short SFD length makes it for the receiver difficult to identify the end of preamble and thus may lead to wrongly detected or missed starting position of data in the signal packet, which may result in significant packet loss and/or energy increase due to packet retransmission. These effects become more serious for low signal-to-noise scenarios, which are typically encountered in ultra low power wireless communications.
Prior art document US2007/086423 is concerned with modified start frame delimiter detection. It mainly tackles the problem that where synchronization is performed using the decoded but not yet de-scrambled received signal, it would be necessary to consume one or more of the bits intended for synchronization in the initialization of a de-scrambler at the receiving system in order to detect the SFD. In the proposed solution the receiving system scans a decoded but not yet de-scrambled received signal for a scrambled version of the SFD associated with the preamble format being used. In this way the availability of these bits for synchronization operations is not lost. In addition, especially where a short preamble is used, it is advantageous that more bits of the preamble are made available for synchronization while still reliably detecting the SFD.
US2005/195770 also deals with frame synchronisation. A system is disclosed for receiving and handling a scrambled input data signal that includes a preamble with a start of frame delimiter (SFD). Instead of performing the SFD search on the descrambled data, the system initiates an SFD search on the scrambled input data, thereby attempting to save an initialization period on the descrambler.
Patent U.S. Pat. No. 5,949,817 discloses a multi-level correlation technique and apparatus for detecting symbol and data frame synchronization in high noise and multi-path environments. Received signals are correlated with known pseudorandom noise (PN) or other known codes at the base level and the base level correlation results are in turn correlated with PN or other known codes at the next higher level, such that the top level of correlation includes all lower levels of encoding in the complete synchronization pattern. The proposed solution provides reliable synchronization detection in low signal-to-noise ratio and/or multi-path environments.
US2009/285269 relates to a method of extracting data from data packets transmitted over a wireless network that includes receiving a data packet having a preamble portion and a payload portion. The preamble portion is cross correlated with a first known spreading sequence to generate a first timing signal and the preamble portion is cross correlated with a second known spreading signal to generate a frame timing signal. An impulse is detected in the first timing signal and a first timing parameter is set based upon the detected impulse in the first timing signal. An impulse is detected in the frame timing signal and a frame timing parameter is set based upon the detected impulse in the frame timing signal. Data is extracted from the received payload portion according to the first timing parameter and the frame timing parameter.